Abstract:

Escherichia coli O104:H4 was associated with a severe foodborne disease outbreak originating in Germany in May 2011.
More than 4000 illnesses and 50 deaths were reported. The outbreak strain was a typical enteroaggregative E. coli (EAEC)
that acquired an antibiotic resistance plasmid and a Shiga-toxin 2 (Stx2)-encoding bacteriophage. Based on whole-genome
phylogenies, the O104:H4 strain was most closely related to other EAEC strains; however, Stx2-bacteriophage are mobile,
and do not necessarily share an evolutionary history with their bacterial host. In this study, we analyzed Stx2-bacteriophage
from the E. coli O104:H4 outbreak isolates and compared them to all available Stx2-bacteriophage sequences. We also
compared Stx2 production by an E. coli O104:H4 outbreak-associated isolate (ON-2011) to that of E. coli O157:H7 strains
EDL933 and Sakai. Among the E. coli Stx2-phage sequences studied, that from O111:H- strain JB1-95 was most closely
related phylogenetically to the Stx2-phage from the O104:H4 outbreak isolates. The phylogeny of most other Stx2-phage
was largely concordant with their bacterial host genomes. Finally, O104:H4 strain ON-2011 produced less Stx2 than E. coli
O157:H7 strains EDL933 and Sakai in culture; however, when mitomycin C was added, ON-2011 produced significantly more
toxin than the E. coli O157:H7 strains. The Stx2-phage from the E. coli O104:H4 outbreak strain and the Stx2-phage from
O111:H- strain JB1-95 likely share a common ancestor. Incongruence between the phylogenies of the Stx2-phage and their
host genomes suggest the recent Stx2-phage acquisition by E. coli O104:H4. The increase in Stx2-production by ON-2011
following mitomycin C treatment may or may not be related to the high rates of hemolytic uremic syndrome associated
with the German outbreak strain. Further studies are required to determine whether the elevated Stx2-production levels are
due to bacteriophage or E. coli O104:H4 host related factors.